Catalysis of methyl viologen radical reactions by polymer-stabilized gold sols

Abstract

The catalysis of methyl viologen radical cation (MV+•) decay reactions by gold sol, stabilized by either poly(vinyl sulfate) (PVS) or poly(vinyl alcohol) (PVA), was studied by pulse radiolysis. Stabilization of the sol by PVS eliminates the hydrogen evolution reaction as a pathway for MV+• decay. This is shown to be due to dimerization of MV"1"• (to the biradical) in the potential field of the polyelectrolyte. On PVA-stabilized sols, the hydrogen evolution reaction is a major pathway although side reactions (probably hydrogenation) interfere to a large extent. The rate of adsorption of MV+• on PVA-stabilized sol is controlled by the diffusion of MV"1"• to the gold particle. Subsequent reactions of protonation and electrochemical desorption, (Au)c""Hm + H30+ -*• (Au)c('1_1)"Hm_1 + H2 + H20, on a slower time scale are the rate-determining steps at the pH range and catalyst concentration used. At higher catalyst concentrations interparticle reaction is invoked to explain the dependence on [Au].(PVS) gold sol has been described previously.12 The other sol was stabilized by poly(vinyl alcohol) (PVA, Polysciences, Inc., 133 000 molecular weight). Approximately 100 mg of HAuC14 was dissolved in 500 mL of 0.1% PVA, and the pH adjusted with NaOH to ~11. CO gas was then bubbled through the solution for 10 min at room temperature. The resultant sol was then acidified with HC104 to pH 2.5 and then boiled for 1 h to expel CO or C02. The sol thus obtained had a spectrum similar to that of the Au/PVS sol previously described.12 Both sols were found

Enhanced alcohol yields in batch cultures of Clostridium acetobutylicum using a three-electrode potentiometric system with methyl viologen as electron carrier

“…1981) but the products of the reaction were not identified: previous work had just shown that they were complex (Hyde and Ledwith, 1974). This MV hydrogenation was observed with different catalysts: gold and nickel electrode (Bowden and Hawkridge, 1981;Meisel et al, 1981) mercury electrode (Tamamushi and Tanaka, 1987) or colloidal platinum (Keller et al, 1980). Our results show that it can occur at carbon electrode.…”

The Surface Chemistry of Hybrid Nanometer-Sized Particles

“…A small blue shift of the plasmon band of Au particles takes place when electron TiO 2 was at a longer wavelength compared to that for aqueous gold sols (514-521 nm) (19). It has been known that density is added to gold particles (21). In contrast, red shift takes place when the electron density transfers from the the surface plasmon band of a metal is often affected by many factors, such as particle size, particle shape, surface metal particles to electron acceptors adsorbed on the particle surface (18a).…”

Formation of silver nanoparticles in formamide:water mixtures: a radiolytic study

“…on reaction with a suitable reducing agent. The blue radical cation shows intense and broad absorption bands in UV-vis range [11,12].…”